This invention relates to an system and method for registering location of a mobile terminal in a mobile communication system, more particularly, to an system and method for making an exchange office recognize a radio zone where the mobile terminal exists to control communication.
Conventionally, methods for making an exchange office control location of a mobile terminal that moves in a plurality of radio zones made up by a plurality of base stations are proposed, for example, one of them is disclosed in Japanese Patent Laid Open No. 71226 (1989).
In this method, a location display unit provided in an exchange office receives location information of a mobile terminal as well as a mobile terminal number and displays the location information of a mobile terminal. Then, location of the mobile terminal is recognized and controlled.
In this conventional location control method, as shown in FIG. 6 for example, a plurality of base stations B1 to B3 are connected with an exchange office A. The base stations make radio zones Z1 to Z3, respectively. A mobile terminal receives one or more control signals from the base stations. If there are multiple control signals, the mobile terminal C registers its location to a base station having transmitted a control signal of which reception level is largest. According to this location registration, the exchange office. A acquires location information of the mobile terminal via a base station having been registered the location. The location information acquired is displayed on the location display unit provided in the exchange office A.
In such a conventional method, when the mobile terminal moves to an area of a base station to which the mobile terminal registers its location overlapped with a neighboring radio zone from an area not overlapped with the neighboring radio zone, if a reception level of signal from the base station having been registered the location is more than a preset level, the mobile terminal does not register its location to the base station of the neighboring radio zone even if the reception level of signal from the neighboring base station is larger than the reception level of signal from the base station to which the mobile terminal registers its location. Therefore, the exchange office A can not recognize that the mobile terminal C has moved to the radio zone of neighboring base station.
To solve this problem, the mobile terminal compares reception levels from a plurality of base stations and register its location to a base station that transmits a signal of largest reception level in the area where radio zones overlap. In this method, the mobile terminal can register its location to the nearest base station, so the exchange office can properly control location of the mobile terminal.
However, in this method, if the mobile terminal is in an area where reception levels from neighboring base stations are nearly equal, the moving mobile terminal may frequently change the base station to be registered location. As a result, it may occur confusion on location control of the mobile terminal.
It is an object of the present invention to solve the aforementioned problems.
It is another object of the present invention to provide a mobile communication system enabling to properly and immediately control location registration of a mobile terminal in an exchange office.
It is still another object of the present invention to provide a method for registering location of a mobile terminal wherein an exchange office can immediately confirm location of a mobile terminal and properly conduct location control of the mobile terminal.
The object of the present invention is achieved by a mobile communication system having a plurality of base stations, each of the base stations makes a radio zone, and a mobile terminal that moves in the radio zones and registers location of the mobile terminal to a predetermined base station, wherein the mobile terminal comprises location registration means for detecting reception levels of signals from the base stations, calculating a difference between a largest reception level and a second largest reception level and registering location of the mobile terminal to a base station having transmitted a signal of the largest reception level when the difference is larger than a preset threshold value.
The object of the present invention is further achieved by a method for registering location of a mobile terminal in a mobile communication system having a plurality of base stations, each of the base stations makes a radio zone, and a mobile terminal that moves in a plurality of radio zones, in the mobile terminal, comprising steps of:
detecting a plurality of reception levels of a plurality of signals from the base stations;
selecting a largest reception level and a second largest reception level from among detected reception levels;
calculating a difference between the largest reception level and the second largest reception level; and
registering location of the mobile terminal to a base station having transmitted a signal of the largest reception level when the difference is lager than a preset threshold value.
In the present invention, changes of location registration are not conducted in an area where reception levels of signals from neighboring base stations are nearly equal and a change of location registration is conducted when a difference of reception levels of signals becomes lager than a preset threshold value as the mobile terminal moves. So the frequency of changing location registration becomes low and confusion of location control in the exchange office becomes avoidable.
Furthermore, the exchange office comprises a location display unit for displaying location of the mobile terminal. The location display unit has a map indicating divisions of the base stations and displays location of the mobile terminal in a division of the base station according to a signal from a base station having been registered location of the mobile terminal. As a result, location of the mobile terminal can be confirmed immediately.